Regasification of LNG requires significant quantities of thermal energy, and typical LNG regasification facilities employ external heat sources to vaporize LNG prior to delivery of the gas to existing pipeline networks. For example, external heat sources include sea water, combustion exhaust, waste heat from power generation, and ambient air. Depending on the particular heat source, the LNG vaporizers may be configured as an open rack seawater vaporizer, a submerged combustion vaporizer, an intermediate fluid vaporizer (e.g., using a glycol-water mixture), or as an ambient air vaporizer. Furthermore, LNG regasification also requires a reliable power supply to operate LNG pumps and compressors for delivery of vaporized LNG product to the pipelines.
More recently, the refrigeration content of LNG is also employed as a heat sink in power generation. For example, power plants may be coupled with LNG regasification, as described in U.S. Pat. Nos. 4,036,028 and 4,231,226 where waste heat from gas turbine exhaust or a thermal power engine is used to vaporize LNG either directly or indirectly (i.e., with or without the use of a heat transfer fluid). Similar configurations are shown in U.S. Pat. No. 6,367,258 where the efficiency of a combined cycle generation plant is increased by integrating LNG vaporization via a heat transfer fluid, which also removes heat from the air intake of a gas turbine to further boost power production. Such configurations are often energy efficient, but generally require integration with an existing power production plant and/or other high-heat source. Similarly, as taught in EP 0 496 283, power is generated by a steam expansion turbine that is driven by a working fluid (here: water) that is heated by a gas turbine exhaust and cooled by a LNG regasification circuit. While such a configuration increases efficiency of a plant to some degree, several problems remain. For example, the utilization of the cryogenic refrigeration content of the LNG is often limited due to the relatively high freezing point of the heat transfer medium. To overcome such difficulties, non-aqueous fluids may be employed as a working fluid in Rankine cycle power generation, which is exemplified in U.S. Pat. No. 4,388,092. Here, a multi-component hydrocarbon fluid is used as working fluid whose composition is altered via distillation to maximize generation efficiency. However, operation and control of such multi-component system is complex, difficult, and often impractical. Similarly, a closed power cycle generation scheme may be employed as described in WO 2006/111957 in which LNG is vaporized using a heat transfer fluid. However, these configurations typically require high circulation rates of the heat transfer fluid and further require a heater to boost the temperature of the vaporized LNG to pipeline specification. Therefore, while some of the known configurations improve efficiency of power generation to some extent, the gain in efficiency is often marginal and rarely justifies the process complexities of such configurations.
Nevertheless, use of LNG refrigeration content as a heat sink in power generation is quite desirable as a typical 500 MMscfd LNG regasification terminal consumes about 10,000 kW that must otherwise be supplied from the external power grid. Where such power source is unreliable, the terminal will also include an internal power plant, which often produces undesirable amounts of waste streams, emissions, and green house gases. Thus, and particularly in an offshore or remote location without reliable power source, operation of an LNG regasification terminal becomes difficult, or even impossible.
Therefore, while various processes and configurations for power generation utilizing LNG as heat sink in regasification are known in the art, all or almost all of them suffer from one or more disadvantages. Thus, there is still a need to provide improved power generation schemes for LNG regasification plants.